Among known fluorine-containing nucleic acid-relating substances, 5-fluorouracil and 5-fluorouridine are well known carcinostatic or antitumor substances.
Derivatives of 5-flourouracil such as the compounds of the formulas: ##STR3## are widely used as carcinostatic or antitumor substances which can suppress side effects of 5-fluorouracil. One of the known processes for preparing these 5-flourouracil derivatives comprises adding a glycoresidue to 5-fluorouracil. According to this process, expensive 5-fluorouracil is not effectively utilized, and this makes the conventional production of the 5-fluorouracil derivatives commercially disadvantageous.
Another known process for preparing 5-Fluorouracil derivatives comprises dehydrating 5,6-dihydro-5-fluoro-6-hydroxyuridine, which has been prepared by reacting uridine with fluorine in water, at a high temperature in the presence of a strong acid such as hydrochloric acid (cf. Japanese Patent Publication (unexamined) No. 28926/1980). According to this process, the obtained product is hardly crystallized probably due to the presence of by-products and it is difficult to improve the purity of the product only by crystallization. Therefore, it must be purified by the use of silica gel and/or cation exchange resin, which is commercially disadvantageous.